Joseph is a recently retired elementary school principal and is a teacher with 36 years of experience in elementary education. He hold an EdS in Advanvced Professional Studies
What's Gravity Got to Do with It?
How high can you throw a ball? Well, no matter how high you throw it, it's going to fall back to the earth. The ball falls back to the ground because there is a force, called gravity, which stops it from flying off into space. Gravity stops you, me, and everything else on the earth from flying off into space and, really, there would be no life on earth without gravity. Think about it for a minute: without gravity, water would not flow out of a bottle, you wouldn't be able to walk or run, fruits wouldn't fall from trees, even the air around us would float away into space!
So if gravity stops objects from leaving the earth, how are scientists able to send rockets and spaceships to the moon and other planets? The answer has to do with escape velocity.
What Is Escape Velocity?
The word 'escape' means to get away from, and 'velocity' here refers to speed, or how fast something travels, so an object's escape velocity is how fast it needs to go the get away from the force of gravity keeping it on the planet. In other words, if we could get something to travel fast enough, it would be able to break away from gravity's pull and fly off into space.
How Does Escape Velocity Work?
Let's imagine you wanted to launch a spaceship from planet earth to the moon. You would need to make enough energy, which comes from your fuel, to get your ship up to a speed of about 25,000 miles per hour in order to leave earth behind. Scientists call this energy thrust. The heavier your spaceship is, the more thrust or energy it will need to reach escape velocity.
Now 25,000 miles per hour is very, very fast and rockets can't get to that speed while they are still in the atmosphere, but when they get off the planet, where the force of earth's gravity is much weaker, they are able to accelerate, or go faster, until they reach escape velocity.
Some Facts About Escape Velocity
The heavier an object is, the more energy it will need to get to its escape velocity. The lighter an object is, the less energy, or thrust, it will need to reach escape velocity.
Weight affects escape velocity, but not size. This means that a small object, like a pen, will need to reach the same escape velocity as something as big as a bus in order to go off into space.
The force of gravity also affects an object's escape velocity. Just as you need less energy to lift something that's light weight than something that is heavy, spaceships need less energy to escape a planet with weak gravity than they do to escape a planet where the force of gravity is strong. So on your way back from the moon, which has weaker gravity than earth, you won't need to travel as fast to get off the surface as you did when you were leaving earth.
Escape velocity is how fast an object needs to be traveling in order to escape the pull of the planet's gravity. On earth, escape velocity is about 25,000 miles per hour. An object must have enough energy, or thrust, to get to its escape velocity. The amount of thrust an object needs depends on the weight of the object and the strength of gravity.
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Escape Velocity Lesson for Kids Quiz
Instructions: Choose an answer and click 'Next'. You will receive your score and answers at the end.
The two main factors that affect the amount of energy an object needs to reach its escape velocity are
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